1. Field of the Invention
The present invention relates to electronic stabilization of a video image, and more particularly, to a method and apparatus for reducing or eliminating jitter in a video image caused from hand shakes in a video camera.
2. Art Background
The reduction in size of video cameras and camcorders has resulted in the availability of hand-held video cameras or camcorders. The size of video cameras provides mobility for a camera-person allowing the video camera to be carried and subjects easily recorded. Although compact and to use, the hand-held video camera is often difficult to hold steady. As result of hand-held shakes from the camera-person, the video output is unstable and such instability results in poor quality video images.
In response to the hand-held video camera shake problem, there have been a number of inventions attempting to stabilize the output video The focus of these inventions has been on stabilizing the physical video camera in order to stabilize the video image. For example, Steadicam.TM.one such system which employs a pair of interconnected spring loaded One end of the arm is pivotally supported by a carrying brace, while the end is connected to a handle which mounts the camera at the center of moment of inertia. The carrying brace is worn by the camera-person, and weight of the camera is counter balanced by action in the spring loaded The Steadicam JR., a portable system, is limited by the weight of video camera. The Steadicam JR will only support camcorders weighing up to approximately 3.5 pounds. Furthermore, the use of the Steady Cam requires skill in order to obtain optimum quality in the video output.
Solid state image sensors, light weight and compact in size, provide advantage over older tube-type imagers. Because of this advantage, solid imagers were developed for applications requiring lightweight and size image sensors such as hand-held video cameras. The two types of state image sensors used in video cameras today are charged coupled (CCD) image sensors and metal oxide semiconductor (MOS) image sensors. In both devices, the image sensor comprises of an array of photosensitive elements. Each element, known as a picture element or pixel, generates a value over an interval of time whereby the value is dependent upon the intensity of light incident upon that photosensitive element. For both and MOS image sensors, the value is a negative charge generated by the photosensitive element. For images sensors compatible with the National Television Standards Committee (NTSC) standard, there may be 768 horizontal pixels and 482 vertical pixels. For image sensors to be for high definition television (HDTV), the array of photosensitive elements be as large as 1920 horizontal and 1035 vertical pixels.
In CCD image sensors, transferring of charge from the photosensitive elements out of the array is accomplished by either frame transfer, transfer, or a combination of the two methods known as frame-interline transfer. In all types of transfer methods, the CCD image sensor uses shift registers. The transfer methods are dependent upon the arrangement the image sensor's vertical registers. The CCD shift register is comprised of p-type silicon material covered with a thin insulating oxide film. On top of oxide layer are electrodes which are connected to clocking control applying a positive voltage to the electrode, the CCD shift register potential well which can store negative charge. By generating a series controlled clocking signals to the electrodes, the charges may be through the shift register and eventually out of the array.
FIG. 1a illustrates a frame transfer CCD image sensor. As shown FIG. 1a, the CCD image sensory is divided into optically sensitive section 10, store section 12 and line readout section 14. After a charge has accumulated in the photosensitive cells in image section 10, charge is transferred into store section 12 very rapidly. Upon transfer charges from image section 10 to store section 12, the photosensitive in store section 12 are emptied for preparation for the next exposure The charge, now stored in store section 12, may be transferred line by line readout section 14 and then gated by output gate 16.
Referring to FIG. 1b, an interline transfer CCD array is In the interline transfer technique, after an initial exposure period of photodiodes 22, charge is transferred from photodiodes 22 to vertical registers 18. In the interline transfer method, the charges are shifted vertical registers 18, and the charges on the bottom of vertical shift registers 18 are transferred into horizontal shift register 20. Then, the charges horizontal shift register 20 are shifted out of the array. In this way, charges are transferred, one at a time, down vertical shift registers then transferred out of the array through horizontal shift line by line.
During high speed transfer of charges from either the image area to stored area in frame transfer, or from the vertical shift registers in interline transfer, the potential wells accumulate extra unwanted charge which generate an effect known as vertical smear. The vertical smear results unwanted line super imposed upon the image. In FIG. 1c, frame interline, a technique which combines the vertical shift registers and field store area, is illustrated. One advantage of the frame interline charge transfer technique is the reduction of vertical smear. The charges are photodiode 22 to vertical registers 26, and then immediately transferred high speed to CCD field memory 28. This high speed transfer reduces the time in which vertical registers 26 may be affected by extra charge accumulation or vertical smear. Once the charges have been transferred field memory section 28, the charges are then transferred out of the CCD image sensor through the horizontal registers in much the same matter as the frame transfer technique.